Comparison of ultrasound-assisted ionic liquid and alkaline pretreatment of Eucalyptus for enhancing enzymatic saccharification

A critical assessment on scalable technologies using high solids loadings in lignocellulose biorefinery: challenges and solutions

The pretreatment and the enzymatic saccharification are the key steps in the extraction of fermentable sugars for further valorization of lignocellulosic biomass (LCB) to biofuels and value-added products via biochemical and/or chemical conversion routes. Due to low density and high-water absorption capacity of LCB, the large volume of water is required for its processing. Integration of pretreatment, saccharification, and co-fermentation has succeeded and well-reported in the literature. However, there are only few reports on extraction of fermentable sugars from LCB with high biomass loading (>10% Total solids-TS) feasible to industrial reality. Furthermore, the development of enzymatic cocktails can overcome technology hurdles with high biomass loading. Hence, a better understanding of constraints involved in the development of technology with high biomass loading can result in an economical and efficient yield of fermentable sugars for the production of biofuels and bio-chemicals with viable titer, rate, and yield (TRY) at industrial scale. The present review aims to provide a critical assessment on the production of fermentable sugars from lignocelluloses with high solid biomass loading. The impact of inhibitors produced during both pretreatment and saccharification has been elucidated. Moreover, the limitations imposed by high solid loading on efficient mass transfer during saccharification process have been elaborated.

Investigation of pre-treatment techniques on spent substrate of Pleurotus ostreatus for enhanced biobutanol production using Clostridium acetobutylicum MTCC 11274

Addressing global energy demand, researchers sought eco-friendly biobutanol production from lignocellulosic waste biomass. In the present research work, five different pre-treatment methods viz., Microwave, Ultrasound, Alkali, Acid, and Hybrid, were investigated to explore its biobutanol production potential by utilizing Pleurotus ostreatus spent as substrate. The compositional and physico-chemical changes of the pre-treated Spent Mushroom Substrate (SMS) were assessed using SEM, FTIR, and XRD. Hybrid pre-treatment (Microwave, Alkali, Ultrasound) showed higher delignification when compared to conventional pre-treatment method. Hybrid pre-treated SMS resulted in higher total reducing sugars (521.53 ± 1.84 mg/g) than indigenous SMS (267.89 ± 1.53 mg/g). Fermentation of hybrid pre-treated SMS with Clostridium acetobutylicum MTCC 11274 produced the highest biobutanol concentration (9.84 ± 0.03 g/L) and yielded 0.38 ± 0.02 g/g of biobutanol. This study revealed that hybrid pre-treatment could be a promising solution for enhanced biobutanol production using SMS biomass.

Bioprospecting CAZymes repertoire of Aspergillus fumigatus for eco-friendly value-added transformations of agro-forest biomass

BACKGROUND

Valorizing waste residues is crucial to reaching sustainable development goals and shifting from a linear fossil-based economy to a circular economy. Fungal cell factories, due to their versatility and robustness, are instrumental in driving the bio-transformation of waste residues. The present work isolated a potent strain, i.e., Aspergillus fumigatus (ZS_AF), from an ancient Złoty Stok gold mine, which showcased distinctive capabilities for efficient hydrolytic enzyme production from lignocellulosic wastes.

RESULTS

The present study optimized hydrolytic enzyme production (cellulases, xylanases, and β-glucosidases) from pine sawdust (PSD) via solid-state fermentation using Aspergillus fumigatus (ZS_AF). The optimization, using response surface methodology (RSM), produced a twofold increase with maximal yields of 119.41 IU/gds for CMCase, 1232.23 IU/gds for xylanase, 63.19 IU/gds for β-glucosidase, and 31.08 IU/gds for FPase. The secretome profiling validated the pivotal role of carbohydrate-active enzymes (CAZymes) and auxiliary enzymes in biomass valorization. A total of 77% of carbohydrate-active enzymes (CAZymes) were constituted by glycoside hydrolases (66%), carbohydrate esterases (9%), auxiliary activities (3%), and polysaccharide lyases (3%). The saccharification of pretreated wheat straw and PSD generated high reducing sugar yields of 675.36 mg/g and 410.15 mg/g, respectively.

CONCLUSION

These findings highlight the significance of an efficient, synergistic, and cost-effective arsenal of fungal enzymes for lignocellulosic waste valorization and their potential to contribute to waste-to-wealth creation through solid-waste management. The utilization of Aspergillus fumigatus (ZS_AF) from an unconventional origin and optimization strategies embodies an innovative approach that holds the potential to propel current waste valorization methods forward, directing the paradigm toward improved efficiency and sustainability.

In-situ growth of electrically conductive MOFs in wood cellulose scaffold for flexible, robust and hydrophobic membranes with improved electrochemical performance

Electrically conductive metal-organic frameworks (EC-MOFs) have attracted great attentions in electrochemical fields, but their practical application is limited by their hard-to-shape powder form. The aims was to integrate continuously nucleated EC-MOFs on natural wood cellulose scaffold to develop biobased EC-MOFs membrane with robust flexibility and improved electrochemical performance for wearable supercapacitors. EC-MOF materials (NiCAT or CuCAT) were successfully incorporated onto porous tempo-oxidized wood (TOW) scaffold to create ultrathin membranes through electrostatic force-mediated interfacial growth and simple room-temperature densification. The studies demonstrated the uniform and continuous EC-MOFs nanolayer on TOW scaffold and the interfacial bonding between EC-MOF and TOW. The densification of EC-MOF@TOW bulk yielded highly flexible ultrathin membranes (about 0.3 mm) with high tensile stress exceeding 180 MPa. Moreover, the 50 %-NiCAT@TOW membrane demonstrated high electrical conductivity (4.227 S·m-1) and hydrophobicity (contact angle exceeding 130°). Notably, these properties remained stable even after twisting or bending deformation. Furthermore, the electrochemical performance of EC-MOF@TOW membrane with hierarchical pores outperformed the EC-MOF powder electrode. This study innovatively anchored EC-MOFs onto wood through facile process, yielding highly flexible membranes with exceptional performance that outperforms most of reported conductive wood-based membranes. These findings would provide some references for flexible and functional EC-MOF/wood membranes for wearable devices.

Efficiency and mechanism in preparation and heavy metal cation/anion adsorption of amphoteric adsorbents modified from various plant straws

Cellulose can be modified for the loading of functional groups such as amino groups, sulfydryl groups, and carboxyl groups. Cellulose-modified adsorbents generally have specific adsorption capacities for either heavy metal anions or cations, and possess the advantages of wide raw material source, high modification efficiency, high adsorbent recyclability, and great convenience in recovery of the adsorbed heavy metals. At present, preparation of amphoteric heavy metal adsorbents from lignocellulose has attracted great attention. However, the difference in efficiency of preparing heavy metal adsorbents by modification of various plant straw materials and mechanism for the difference remain to be further explored. In this study, three plant straws, including Eichhornia crassipes (EC), sugarcane bagasse (SB) and metasequoia sawdust (MS), were sequentially modified by tetraethylene-pentamine (TEPA) and biscarboxymethyl trithiocarbonate (BCTTC) to obtain amphoteric cellulosic adsorbents (EC-TB, SB-TB and MS-TB, respectively), which can simultaneously adsorb heavy metal cations or anions. The heavy metal adsorption properties and mechanism before and after modification were compared. Pb(II) and Cr(VI) removal rates by the three adsorbents were 2.2-4.3 folds and 3.0-13.0 folds of those before modification, respectively, following the order of MS-TB > EC-TB > SB-TB. In the five-cycle adsorption-regeneration test, the Pb(II) and Cr(VI) removal rate by MS-TB decreased by 58.1 % and 21.5 %, respectively. Among the three plant straws, MS possessed the most abundant hydroxyl groups and the largest specific surface area (SSA), and accordingly MS-TB had the highest load of adsorption functional groups [(C)NH, (S)CS and (HO)CO] and also the largest SSA among the three adsorbents, which contribute to its highest modification and adsorption efficiency. This study is of great significance for screening suitable raw plant materials to prepare amphoteric heavy metal adsorbents with superior adsorption performance.

Cellulosic Ethanol Production from Weed Biomass Hydrolysate of Vietnamosasa pusilla

Lignocellulosic biomass can be used as a renewable and sustainable energy source to help reduce the consequences of global warming. In the new energy age, the bioconversion of lignocellulosic biomass into green and clean energy displays remarkable potential and makes efficient use of waste. Bioethanol is a biofuel that can diminish reliance on fossil fuels while minimizing carbon emissions and increasing energy efficiency. Various lignocellulosic materials and weed biomass species have been selected as potential alternative energy sources. Vietnamosasa pusilla, a weed belonging to the Poaceae family, contains more than 40% glucan. However, research on the applications of this material is limited. Thus, here we aimed to achieve maximum fermentable glucose recovery and bioethanol production from weed biomass (V. pusilla). To this end, V. pusilla feedstocks were treated with varying concentrations of H₃PO₄ and then subjected to enzymatic hydrolysis. The results indicated that after pretreatment with different concentrations of H₃PO₄, the glucose recovery and digestibility at each concentration were markedly enhanced. Moreover, 87.5% of cellulosic ethanol was obtained from V. pusilla biomass hydrolysate medium without detoxification. Overall, our findings reveal that V. pusilla biomass can be introduced into sugar-based biorefineries to produce biofuels and other valuable chemicals.

Challenges and perspectives of green-like lignocellulose pretreatments selectable for low-cost biofuels and high-value bioproduction

Lignocellulose represents the most abundant carbon-capturing substance that is convertible for biofuels and bioproduction. Although biomass pretreatments have been broadly applied to reduce lignocellulose recalcitrance for enhanced enzymatic saccharification, they mostly require strong conditions with potential secondary waste release. By classifying all major types of pretreatments that have been recently conducted with different sources of lignocellulose substrates, this study sorted out their distinct roles for wall polymer extraction and destruction, leading to the optimal pretreatments evaluated for cost-effective biomass enzymatic saccharification to maximize biofuel production. Notably, all undigestible lignocellulose residues are also aimed for effective conversion into value-added bioproduction. Meanwhile, desired pretreatments were proposed for the generation of highly-valuable nanomaterials such as cellulose nanocrystals, lignin nanoparticles, functional wood, carbon dots, porous and graphitic nanocarbons. Therefore, this article has proposed a novel strategy that integrates cost-effective and green-like pretreatments with desirable lignocellulose substrates for a full lignocellulose utilization with zero-biomass-waste liberation.

Investigation of a robust pretreatment technique based on ultrasound-assisted, cost-effective ionic liquid for enhancing saccharification and bioethanol production from wheat straw

Application of cost-effective pretreatment of wheat straw is an important stage for massive bioethanol production. A new approach is aimed to enhance the pretreatment of wheat straw by using low-cost ionic liquid [TEA][HSO₄] coupled with ultrasound irradiation. The pretreatment was conducted both at room temperature and at 130 °C with a high biomass loading rate of 20% and 20% wt water assisted by ultrasound at 100 W-24 kHz for 15 and 30 min. Wheat straw pretreated at 130 °C for 15 and 30 min had high delignification rates of 67.8% and 74.9%, respectively, and hemicellulose removal rates of 47.0% and 52.2%. Moreover, this pretreatment resulted in producing total reducing sugars of 24.5 and 32.1 mg/mL in enzymatic saccharification, respectively, which corresponds to saccharification yields of 67.7% and 79.8% with commercial cellulase enzyme CelluMax for 72 h. The ethanol generation rates of 38.9 and 42.0 g/L were attained for pretreated samples for 15 and 30 min, equivalent to the yields of 76.1% and 82.2% of the maximum theoretical yield following 48 h of fermentation. This demonstration provided a cheap and promising pretreatment technology in terms of efficiency and shortening the pretreatment time based on applying low-cost ionic liquid and efficient ultrasound pretreatment techniques, which facilitated the feasibility of this approach and could further develop the future of biorefinery.

Phenol Liquefaction of Waste Sawdust Pretreated by Sodium Hydroxide: Optimization of Parameters Using Response Surface Methodology

In this study, a two-step method was used to realize the liquefaction of waste sawdust under atmospheric pressure, and to achieve a high liquefaction rate. Specifically, waste sawdust was pretreated with NaOH, followed by liquefaction using phenol. The relative optimum condition for alkali-heat pretreatment was a 1:1 mass ratio of NaOH to sawdust at 140 °C. The reaction parameters including the mass ratio of phenol to pretreated sawdust, liquefaction temperature, and liquefaction time were optimized by response surface methodology. The optimal conditions for phenol liquefaction of pretreated sawdust were a 4.21 mass ratio of phenol to sawdust, a liquefaction temperature of 173.58 °C, and a liquefaction time of 2.24 h, resulting in corresponding liquefied residues of 6.35%. The liquefaction rate reached 93.65%. Finally, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) were used to analyze untreated waste sawdust, pretreated sawdust, liquefied residues, and liquefied liquid. SEM results showed that the alkali-heat pretreatment and liquefaction reactions destroyed the intact, dense, and homogeneous sample structures. FT-IR results showed that liquefied residues contain aromatic compounds with different substituents, including mainly lignin and its derivatives, while the liquefied liquid contains a large number of aromatic phenolic compounds. XRD showed that alkali-heat pretreatment and phenol liquefaction destroyed most of the crystalline regions, greatly reduced the crystallinity and changed the crystal type of cellulose in the sawdust.

Extraction, Isolation, and Purification of Value-Added Chemicals from Lignocellulosic Biomass

This review covers the operating conditions for extracting top value-added chemicals, such as levulinic acid, lactic acid, succinic acid, vanillic acid, 3-hydroxypropionic acid, xylitol, 2,5-furandicarboxylic acid, 5-hydroxymethyl furfural, chitosan, 2,3-butanediol, and xylo-oligosaccharides, from common lignocellulosic biomass. Operating principles of novel extraction methods, beyond pretreatments, such as Soxhlet extraction, ultrasound-assisted extraction, and enzymatic extraction, are also presented and reviewed. Post extraction, high-value biochemicals need to be isolated, which is achieved through a combination of one or more isolation and purification steps. The operating principles, as well as a review of isolation methods, such as membrane filtration and liquid–liquid extraction and purification using preparative chromatography, are also discussed.

Surfactant-assisted alkaline pretreatment and enzymatic hydrolysis of Miscanthus sinensis for enhancing sugar recovery with a reduced enzyme loading

Surfactants play a vital role in the delignification and saccharification of lignocellulosic biomass. A strategy for coupling surfactant-assisted alkaline pretreatment (SAP) with surfactant-assisted enzymatic hydrolysis (SEH) has been proposed for improving sugar recovery from a potential energy crop, Miscanthus sinensis. Poly (ethylene glycol) 2000 (PEG 2000) was found to be more efficient in SAP than in other tested surfactants. Compositional and structural analysis revealed that the SAP process with 1% of PEG 2000 produced more efficient lignin removal and microstructure disruption of the pretreated sample, thus indicating much higher reducing sugar yields of 544.4–601.2 mg/g compared to the samples that were untreated or pretreated by alkali alone. Moreover, SEH with 1% Tween 80, which could block the lignin-enzyme interactions, produced a substantial reduction of 33.3% in the enzyme loading to achieve a higher sugar recovery from the SAP sample.

Effect of microwave/hydrothermal combined ionic liquid pretreatment on straw: Rumen anaerobic fermentation and enzyme hydrolysis

To explore green technology for wheat straw pretreatment, this study combined the microwave or hydrothermal with ionic liquid ([Bmim][OAc]) on wheat straw followed by rumen fermentation. The optimal conditions of microwave assisted ionic liquids pretreatment (M-I) and hydrothermal assisted ionic liquids pretreatment (H-I) treatment were 360 W and 200 °C, and the corresponding lignin removal rates reached 35.3% and 25.4%, respectively. Rumen fermentation showed that the highest volatile fatty acid (VFA) yield was found in M-I group, followed by H-I group at 234 and 180 mg/g, respectively. As for enzymatic hydrolysis, the saccharification rates at 3 days of M-I (360 W) and H-I (200 °C) were determined to be 393 and 320 mg/g. The optimal ionic liquid dosage was determined to be 30% in consideration of cost and VFA conversion rate. M-I pretreatment plus the rumen fermentation enjoyed the benefit of no enzyme addition and high product recovery, which was worth further investigating.

Enhanced Saccharification of Purple Alfalfa via Sequential Pretreatment with Acidified Ethylene Glycol and Urea/NaOH

Purple Alfalfa is an inexpensive, abundant, readily available lignocellulosic material. This work was attempted to develop an efficient combination pretreatment by sequential HClO4–ethyl glycol–H2O (1.2:88.8:10, w/w/w) extraction at 130 °C in 0.5 h and urea/NaOH (urea 12 wt%, NaOH 7 wt%) soaking at −20 °C for 0.5 h for the pretreatment of purple alfalfa. The porosity, morphology, and crystallinity of pretreated purple alfalfa were characterized with SEM, FM, XRD, and FTIR. This combination pretreatment had a significant influence on hemicellulose removal and delignification. The above changes could enhance cellulose accessibility to enzymes and improve the enzymatic digestibility of cellulose. High yields of reducing sugars from pretreated purple alfalfa were obtained at 93.4%. In summary, this combination pretreatment has high potential application in the future.

Transforming lignocellulosic biomass into biofuels enabled by ionic liquid pretreatment

Processes that can convert lignocellulosic biomass into biofuels and chemicals are particularly attractive considering renewability and minimal environmental impact. Ionic liquids (ILs) have been used as novel solvents in the process development in that they can effectively deconstruct recalcitrant lignocellulosic biomass for high sugar yield and lignin recovery. From cellulose-dissolving ILs to choline-based and protic acidic ILs, extensive research in this field has been done, driven by the promising future of IL pretreatment. Meanwhile, shortcomings and technological hurdles are ascertained during research and developments. It is necessary to present a general overview of recent developments and challenges in this field. In this review paper, three aspects of advances in IL pretreatment are critically analyzed: biocompatible ILs, protic acidic ILs and combinatory pretreatments.

Enhancement of biomass conservation and enzymatic hydrolysis of rice straw by dilute acid-assisted ensiling pretreatment

To reduce the cost of lignocellulosic pretreatment, rice straw was ensiled with dilute formic acid (FA, 0, 0.2, 0.4, and 0.6%) for 3, 6, 9, 15 and 30 days, and evaluated its effects on fermentation dynamics, lignocellulosic degradation and enzymatic hydrolysis. The results showed that the application of FA, especially at 0.6% level, reduced total fermentation losses of the resulting silages, as evidenced by low dry matter loss, ammonia nitrogen and ethanol content. Meanwhile, the 0.6% FA application promoted hemicellulose removal (232.41 vs 187.52 g/kg DM) and xylose production (0.35 vs 2.80 g/kg DM). The glucose yield and cellulose convertibility of rice straw increased after 30 days of ensiling, and further enhanced by the 0.6% FA application. In conclusion, the 0.6% FA-assisted ensiling pretreatment improved both biomass preservation, hemicellulose removal and enzymatic hydrolysis of rice straw, which is beneficial to the subsequent biofuel production chain.

Ultrasound enhanced biosynthesis of L-theanine from L-glutamine and ethylamine by recombinant γ-glutamyltranspeptidase

A mutant library of the key amino acid residue site E387 in γ-glutamyltranspeptidase was constructed to screen the mutant enzymes with significantly improved thermal stability (E387Q). The reaction temperature of the mutant enzyme (E387Q) was 10℃ higher than that of the parent enzyme. Ultrasound-assisted synthesis of L-theanine by γ-glutamyltranspeptidase was investigated. The effects of ultrasonic power, reaction pH and substrate concentration on the enzymatic synthesis of L-theanine were studied by the response surface method. The results showed that the optimal process conditions are ultrasonic power of 100 W, reaction pH of 9, substrate L-glutamine concentration of 120 mmol/L, reaction temperature of 45℃, and L-theanine yield of 89.1%. The yield of L-theanine is 2.61 times higher than that obtained without ultrasound. Ultrasound can significantly promote the synthesis of L-theanine by γ-glutamyltranspeptidase.

Enhancing the Enzymatic Saccharification of Grain Stillage by Combining Microwave-Assisted Hydrothermal Irradiation and Fungal Pretreatment

Grain stillage from the liquor industry was pretreated by using microwave-assisted hydrothermal pretreatment, fungal pretreatments, and their combination to enable efficient enzymatic hydrolysis for sugar production. The microwave-assisted hydrothermal (MH) pretreatment was optimized by using a response surface methodology, and the respective maximum reducing sugar yield and saccharification efficiency of 17.59 g/100 g and 33.85%, respectively, were achieved under the pretreatment conditions of microwave power = 120 W, solid-to-liquid ratio = 1:15 (g·mL^-1), and time = 3.5 min. The fungal pretreatment with Phanerochaete chrysosporium digestion (PC) achieved the maximum ligninolytic enzyme activities in 6 days with 10% inoculum size at which the reducing sugar yield and saccharification efficiency reached 19.74 g/100 g and 36.29%, respectively. To further improve the pretreatment efficiency, MH and PC pretreatments were combined, but the sequence of MH and PC mattered on the saccharification efficiency. The MH + PC pretreatment (the MH prior to the PC) was better than PC + MH (the PC prior to the MH) in terms of saccharification efficiency. Overall, the MH + PC pretreatment achieved superior reducing sugar yield and saccharification efficiency (25.51 g/100 g and 66.28%, respectively) over all other studied pretreatment methods. The variations of chemical compositions and structure features of the raw and pretreated grain stillage were characterized by using scanning electron microscopy and Fourier transform infrared spectroscopy. The results reveal that both MH and PC pretreatments mainly functioned on delignification and decreasing cellulose crystallinity, thus enhancing the enzymatic saccharification of the pretreated grain stillage. The combined MH and PC pretreatment could be a promising method to enable cost-efficient grain stillage utilization for downstream applications such as biofuels.

A Two-Step Ferric Chloride and Dilute Alkaline Pretreatment for Enhancing Enzymatic Hydrolysis and Fermentable Sugar Recovery from Miscanthus sinensis

A two-step process was proposed to enhance enzymatic hydrolysis of Miscanthus sinensis based on a comparative study of acid/alkaline pretreatments. Ferric chloride pretreatment (FP) effectively removed hemicellulose and recovered soluble sugars, but the enzymatic hydrolysis was not efficient. Dilute alkaline pretreatment (ALP) resulted in much better delignification and stronger morphological changes of the sample, making it more accessible to enzymes. While ALP obtained the highest sugar yield during enzymatic hydrolysis, the soluble sugar recovery from the pretreatment stage was still limited. Furthermore, a two-step ferric chloride and dilute alkaline pretreatment (F-ALP) has been successfully developed by effectively recovering soluble sugars in the first FP step and further removing lignin of the FP sample in the second ALP step to improve its enzymatic hydrolysis. As a result, the two-step process yielded the highest total sugar recovery (418.8 mg/g raw stalk) through the whole process.

Investigation of alkaline hydrogen peroxide pretreatment to enhance enzymatic hydrolysis and phenolic compounds of oil palm trunk

Alkaline hydrogen peroxide (AHP) as a pretreatment effectively enhances the increasing enzymatic digestibility of oil palm trunk (OPT) for conversion to biofuels and bioproducts in the biorefinery processes. The effect of hydrogen peroxide concentration (1-5%), temperature (50-90 °C), and time (30-90 min) were studied to find out the optimum condition for the removal of lignin. The optimum condition attained at 70 °C, 30 min, and 3% H₂O₂ g /g of biomass not only increased the cellulose content from 38.67% in raw material to 73.96% but also removed lignin and hemicellulose up to 50% and 57.12%, respectively. The AHP-treated fibers subjected to enzyme hydrolysis showed significant improvement in glucose concentration that increased from 11.77 (± 0.84) g/L (raw material) to 46.15 (± 0.32) g/L with 59.82% enzyme digestibility at 96 h. Scanning electron microscopy (SEM) and Fourier transformation infrared (FT-IR) were employed to analyze the morphology and structural changes of untreated and AHP-treated fibers. SEM results showed disruption of the intact OPT structure resulting in increase of enzyme accessibility to cellulose. The FT-IR identified changes in peaks which indicated structural transformation and dissolution of both lignin and hemicellulose molecules caused by AHP treatment. The black liquor obtained from AHP treatment contained about 5.13 mg gallic acid equivalent (GAE)/g of dry sample of total phenolic content (TPC) and an antioxidant activity of 59.80% and 65.51% inhibitions of DPPH and ABTS assays, respectively. Hence, it is a sustainable approach to utilize waste for the recovery of multiple value-added products during pretreatment process.

An evaluation of sonication pretreatment for enhancing saccharification of brewers' spent grain

This paper deals with the investigation of ultrasound (US) pretreatment of brewer's spent grain (BSG) as a means of releasing fermentable sugars, and the subsequent production of ethanol from this lignocellulosic biomass. Using response surface methodology (RSM), the influence of US power, time, temperature and biomass loading on fermentable sugar yield from BSG was studied. The optimal conditions were found to be 20% US power, 60 min, 26.3 °C, and 17.3% w/v of biomass in water. Under these conditions, an approximate 2.1-fold increase in reducing sugar yield (325 ± 6 mg/g of biomass) was achieved, relative to untreated BSG (151.1 ± 10 mg/g of biomass). In contrast to acid or alkaline pretreatment approaches, the use of water obviated the need for neutralization for the recovery of sugars. The characterization of native and pretreated BSG was performed by HPLC, FTIR, SEM and DSC. Fermentation studies using S. cerevisiae growing on pretreated BSG resulted in a conversion of 66% of the total sugar content ininto ethanol with an ethanol content of 17.73 ± 2 g/ 100 g of pretreated BSG. These results suggest that ultrasound pretreatment is a promising technology for increased valorization of BSG as a feedstock for production of bioethanol, and points ton the need for further work in this area.

Pretreatment and fermentation of lignocellulosic biomass: reaction mechanisms and process engineering

At a time of rapid depletion of oil resources, global food shortages and solid waste problems, it is imperative to encourage research into the use of appropriate pre-treatment techniques using regenerative raw materials such as lignocellulosic biomass.

Ultrasound and surfactant assisted ionic liquid pretreatment of sugarcane bagasse for enhancing saccharification using enzymes from an ionic liquid tolerant Aspergillus assiutensis VS34

Ionic liquid (IL) pretreatment represents an effective strategy for effective fractionation of lignocellulosic biomass (LB) to fermentable sugars in a biorefinery. Optimization of combinatorial pretreatment of sugarcane bagasse (SCB) with IL (1-butyl-3-methylimidazolium chloride [Bmim]Cl) and surfactant (PEG-8000) resulted in enhanced sugar yield (16.5%) upon enzymatic saccharification. The saccharification enzymes (cellulase and xylanase) used in the current study were in-house produced from a novel IL-tolerant fungal strain Aspergillus assiutensis VS34, isolated from chemically polluted soil, which produced adequately IL-stable enzymes. This is the first ever report of IL-stable cellulase/xylanase enzyme from Aspergillus assiutensis. To get the mechanistic insights of combinatorial pretreatment physicochemical analysis of variously pretreated biomass was executed using SEM, FT-IR, XRD, and ¹H NMR studies. The combined action of IL, surfactant and ultrasound had very severe and distinct effects on the ultrastructure of biomass that subsequently resulted in enhanced accessibility of saccharification enzymes to biomass, and increased sugar yield.

Comparison of Fenton and bismuth ferrite Fenton-like pretreatments of sugarcane bagasse to enhance enzymatic saccharification

This study compared enzymatic saccharification of sugarcane bagasse (SCB) after application of two different pretreatment methods, Fenton pretreatment (FP) and BiFeO₃ Fenton-like pretreatment (BFP). The composition, morphology and structural properties of SCB with different pretreatments were analyzed. Results showed that, after BFP, the yield of reducing sugar of SCB under enzymatic saccharification for 72 h was 25.8%, and the sugar conversion rate was 36.6%, which were 2.2 and 2.4-fold those of the FP, respectively. Moreover, the removal of hemicellulose and delignification in the BFP was more severe than that in the FP. The determination of hydroxyl radical (OH) in the two different Fenton processes revealed that the OH generated in the BiFeO₃ Fenton-like system was higher in concentration and longer in action time than that in the Fenton system, which was likely key to the stronger effect of BFP than FP on the enzymatic saccharification of SCB.

Enhanced Enzymatic Hydrolysis of Pennisetum alopecuroides by Dilute Acid, Alkaline and Ferric Chloride Pretreatments

In this study, effects of different pretreatment methods on the enzymatic digestibility of Pennisetum alopecuroides, a ubiquitous wild grass in China, were investigated to evaluate its potential as a feedstock for biofuel production. The stalk samples were separately pretreated with H₂SO₄, NaOH and FeCl₃ solutions of different concentrations at 120 °C for 30 min, after which enzymatic hydrolysis was conducted to measure the digestibility of pretreated samples. Results demonstrated that different pretreatments were effective at removing hemicellulose, among which ferric chloride pretreatment (FCP) gave the highest soluble sugar recovery (200.2 mg/g raw stalk) from the pretreatment stage. In comparison with FCP and dilute acid pretreatment (DAP), dilute alkaline pretreatment (DALP) induced much higher delignification and stronger morphological changes of the biomass, making it more accessible to hydrolysis enzymes. As a result, DALP using 1.2% NaOH showed the highest total soluble sugar yield through the whole process from pretreatment to enzymatic hydrolysis (508.5 mg/g raw stalk). The present work indicates that DALP and FCP have the potential to enhance the effective bioconversion of lignocellulosic biomass like P. alopecuroides, hence making this material a valuable and promising energy plant.

Ultrasound combined with dilute acid pretreatment of grass for improvement of fermentative hydrogen production

In this study, the dilute acid pretreatment combined with ultrasound was applied to improve fermentative hydrogen production from grass. The experimental results indicated that SCOD and soluble carbohydrate contents of grass was improved by 98.6% and 236.9% after the combined treatment, respectively. Surface morphology (SEM and AFM) and crystallinity analysis revealed that the combined pretreatment process could effectively destroyed the biomass structure and increased their surface area. Owing to the increased soluble organics proportion and better enzymatic accessibility of residual solids, the hydrogen yield reached 42.2 mL/g-dry grass after the combined treatment, which was 311.7%, 190.0% and 35.0% higher in comparison with the control, individual ultrasound and acid pretreated groups, respectively. Meanwhile, the combined treatment also increased the substrate utilization efficiency and induced a more efficient fermentation pathway. Bacterial community analysis revealed that more enrichment of Clostridium and less enrichment of Enterococcus contributed to the improved hydrogen production.

Physicochemical characteristics and pyrolysis performance of corn stalk torrefied in aqueous ammonia by microwave heating

The physicochemical characteristics and pyrolysis performance of corn stalk (CS) torrefied in water and aqueous ammonia by microwave heating were investigated. Physicochemical characterization revealed that both microwave water torrefied CS (MCS) and microwave ammonia torrefied CS (MACS) showed low hemicellulose content, disrupted macrostructure, improved porous properties, and low ash content. MACS exhibited a significantly lower crystallinity degree of 44.34% than CS (79.55%) and MCS (89.50%). MACS also showed increased methyl/methylene groups intensity, and complete acetyl groups disrupture. Pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) revealed that compared with CS and MCS, MACS exhibited higher peak areas for ketones, aldehydes, furans and esters, and significantly lower peak areas for acids and phenols. A possible mechanism was proposed for the effects of wet torrefaction with aqueous ammonia on changes in physicochemical structure and pyrolysis behavior of corn stalk.

A microwave-assisted aqueous ionic liquid pretreatment to enhance enzymatic hydrolysis of Eucalyptus and its mechanism

A novel pretreatment strategy based on combination of microwave and ionic liquid [TBA][OH] was developed for enhancing enzymatic hydrolysis of Eucalyptus sawdust. The sugar yield of pretreated sample achieved 410.67 mg/g in 48 h, which suffered from optimized microwave-assisted [TBA][OH] pretreatment. The work mechanism was illuminated by chemical composition, Fourier transform infrared spectroscopy (FTIR), ¹³C cross polarization/magic-angle spinning solid state NMR (¹³C solid NMR), X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses. The combined effect of microwave and [TBA][OH] leads to the violent deconstruction of lignin, removal of hemicelluloses, destruction of crystalline region and an eroded, pored and irregular micro-morphology. As a green, relatively inexpensive and high efficient pretreatment, microwave-assisted [TBA][OH] pretreatment has great potential in the field of bio-refinery.

Development of co-immobilized tri-enzyme biocatalytic system for one-pot pretreatment of four different perennial lignocellulosic biomass and evaluation of their bioethanol production potential

Today, many researchers are focusing on research for alternative promising energy sources and sustainable technology for bioethanol production to meet the increasing global energy demand. Here, we develop a novel one-pot pretreatment technology by co-immobilizing laccase, cellulase and β-glucosidase to act as a tri-enzyme biocatalyst for evaluating the bioethanol production potential of four sustainable lignocellulosic biomasses viz., Typha angustifolia, Arundo donax, Saccharum arundinaceum, and Ipomoea carnea. The co-immobilized enzyme system was more stable at different temperatures and at longer storage, compared to free enzyme. During enzymatic saccharification, Saccharum arundinaceum showed higher total reducing sugar of 205 ± 3.73 mg/g when compared to other biomass. The highest percentage of bioethanol yield of 63.43 ± 9.35% was obtained with Ipomoea carnea. The effects of co-immobilized tri-enzyme biocatalyst on the biomasses were evaluated. The results revealed that the co-immobilized tri-enzyme biocatalyst could act as effective one-pot pretreatment for the production of bioethanol from lignocellulosic biomass.

Pretreatment with concurrent UV photocatalysis and alkaline H2O2 enhanced the enzymatic hydrolysis of sisal waste

This work studied a concurrent UV photocatalysis and alkaline H₂O₂ pretreatment (UHP) to enhance the subsequent enzymatic hydrolysis of sisal waste in comparison with alkaline H₂O₂ pretreatment (AHP). An optimal condition was identified for UHP at H₂O₂ charge 0.1 g/g dried sisal waste, pH 10.0, and UV radiation for 6 h. Under this condition, UHP led to a delignification rate of 76.6%, a conversion to reducing sugar at 71.2%, and a conversion to glucose at 91.6%, respectively. XRD, FT-IR and SEM analysis showed an increase in crystalline degree and significant changes in the structure of sisal during UHP. The current study implicates that UHP is more efficient than AHP in pretreating sisal waste, with reduced H₂O₂ charge, shortened pretreatment time, and enhanced enzymatic digestibility.